1. Field of the Invention:
This invention relates to a scroll-type fluid transferring machine to be used as a compressor such as a refrigerant compressor, an air compressor, and so forth; a fluid pump; a turbine expanding machine; and others.
2. Discussion of the Background:
In the following, explanations will be given as to the conventional scroll-type fluid transferring machine by taking a compressor as an example.
First of all, the principle of the scroll compressor will be explained briefly.
FIGS. 1(a) to 1(d) of the accompanying drawing illustrate the fundamental structural elements of the scroll compressor and the theory of its compression. In the drawing, a reference numeral 1 designates a stationary scroll member, a reference numeral 2 indicates an orbiting scroll member, a numeral 3 refers to an outlet port, and a numeral 4 refers to a compression chamber. A reference letter O designates a fixed point on the stationary scroll member 1, while a reference letter 0' denotes a fixed point on the orbiting scroll member 2. Both stationary scroll member 1 and orbiting scroll member 2 are respectively in the form of a wrap 1a and a wrap 2a, each being constructed with an involute curve, an arc, and so forth of the same shape, but being in a mutually opposite winding direction.
In the following discussion, the operation of this type of the scroll compressor will be explained. The stationary scroll member 1 is in the stationary state with respect to the open space, while the orbiting scroll member 2 is combined with the stationary scroll member 1 and changes its position at the respective moving angles of 0.degree., 90.degree., 180.degree. and 270.degree., as shown in FIGS. 1(a), 1(b), 1(c) and 1(d) respectively, without changing its posture with respect to the open space. With the movement of the orbiting scroll member 2, the compression chamber 4 in the form of a crescent defined between the wrap 1a of the stationary scroll member 1 and the wrap 2a of the orbiting scroll member 2 sequentially reduces its volume, whereby a gas confined in this compression chamber 4 is compressed and discharged from the outlet port 3. During this compression stroke, a distance between the fixed points O--O' in FIGS. 1(a) to 1(d) is maintained constant, and, if a space interval between the wraps is taken as a and the thickness of each of them is denoted as t, the distance (O--O') is represented as O--O'=a/2-t. Additionally, the space interval a corresponds to a pitch of the wrap.
The explanations given above are the outlines of the apparatus known as a scroll compressor.
In the following discussion, explanations will be given as to a concrete construction and operations of the conventional scroll compressor.
FIG. 2 is a side elevational view in longitudinal cross-section showing a compressing mechanical part of a conventional scroll compressor. In FIG. 2, a reference numeral 1 designates a stationary scroll member constructed with a wrap 1a such as in an involute form; a base plate (or ceiling plate) 1b, from one surface side of which the wrap 1a is projected downward; an outlet port 3 formed in one part of this base plate 1b; and an inlet port 5 formed in another part thereof. A numeral 2 refers to an orbiting scroll member constructed with a wrap 2a in the same shape as that of the wrap 1a of the stationary scroll member 1, but wound in an opposite direction to that of the wrap 1a; a base plate (or bottom plate) 2b, from one surface side of which the wrap 2a is projected outward; and a boss 13 projected downward from the other surface of the base plate 2b. A reference numeral 4 represents a compression chamber defined by the wrap 1a of the stationary scroll member 1, the base plate 1b, the wrap 2a of the orbiting scroll member 2, and the base plate 2b. A numeral 6 refers to a bearing frame, a numeral 7 refers to a thrust bearing provided on the bearing frame 6 to hold the bottom surface of the base plate 2b of the orbiting scroll member 2, and a numeral 8 refers to a main shaft having an eccentric bore 14, into which the boss 13 of the orbiting scroll member 2 is fitted in a freely rotatable manner. A reference numeral 9 denotes a rotation-preventing mechanism constructed with an Oldham's coupling, and so forth, which functions to prevent the orbiting scroll member 2 from its rotation around the boss 13 as its shaft and to cause it to revolve around the main shaft 8 as its crank shaft. A numeral 10 refers to a balancer. These are the principal components for the compression mechanical part of the scroll compressor. In this mechanical structure, the wrap 2a of the orbiting scroll member 2 and the wrap 1a of the stationary scroll member 1 are fitted together in a mutually opposite relationship, and the boss 13 of the orbiting scroll member 2 is fitted into the eccentric bore 14 of the main shaft 8. The main shaft 8 is supportively fitted in the bearing frame 6 in a freely rotatable manner, both bearing frame 6 and the stationary scroll member 1 being coupled together with screw-threaded bolts, etc. (not shown in the drawing). Furhter, the upper surface of the thrust bearing 7 mounted on the bearing frame 6 and the bottom surface of the base plate 2b of the orbiting scroll member 2 opposite to the wrap 2a come into contact each other. The balancer 10 is fixed on one part of the main shaft 8 by pressing-fitting.
FIG. 3(a) through 6(b) are schematic diagrams for explaining the function of various thrust bearing sliding parts of conventional scroll compressors, wherein FIGS. 3(a), 4(a), 5(a) and 6(a) respectively illustrate a state, in which a gas pressure is not present in the compressor before or after its operation, while FIGS. 3(b), 4(b), 5(b) and 6(b) respectively show a state, in which the base plate 2a of the orbiting scroll member 2 is deformed by a thrust load imparted to it during operation of the compressor. It should be noted that, throughout FIGS. 3(a) to 6(b), reference letters .delta..sub.1 to .delta..sub.3 denote a quantity of displacement of the base plate 2b of the orbiting scroll member 2 or a difference in height in the axial direction between the inner peripheral side and the outer peripheral side of hte thrust bearing 7.
FIGS. 3(a) and 3(b) illustrate a case, wherein the bottom surface of the base plate 2b of the orbiting scroll member 2 constituting the sliding surface with the upper surface of the thrust bearing 7 (in other words, the upper surface of the thrust bearing 7 constituting the sliding surface with the bottom surface of the above-mentioned base plate 2b) is perpendicular to the direction of the axis, in the form of their constituent parts; that is to say, the inner peripheral side and the outer peripheral side of the thrust bearing constituting the sliding surface are in the horizontal plane.
FIGS. 4(a) and 4(b) illustrate a case, wherein the inner peripheral side of the upper surface of the thrust bearing 7 is in the form of a center-convex by an amount .delta..sub.2 with respect to the outer peripheral side thereof.
FIGS. 5(a) and 5(b) illustrate a case, wherein the bottom surface of the base plate 2b of the orbiting scroll member 2 is in a center-convexed shape at the inner peripheral side of the thrust bearing 7 by an amount .delta..sub.3 with respect to the outer peripheral side thereof as shown in more detail in FIG. 7.
FIGS. 6(a) and 6(b) show a state, in which the upper surface of the thrust bearing 7 is in a center-convexed shape by an amount .delta..sub.2 as is the case with FIGS. 4(a) and 4(b), and, at the same time, the bottom surface of the base plate 2b of the orbiting scroll member 2 is in the center-convexed shape by an amount .delta..sub.3 as is the case with FIGS. 5(a) and 5(b).
Incidentally, it should be noted that each of FIGS. 3(a) through 7 is exaggerated in its illustration of the thrust bearing 7 and the base plate 2b of the orbiting scroll member 2 in their axial direction for better understanding of the explanations.
In the following discussion, an explanation will be made as to the operations of the scroll compressor which is constructed in the above-described manner. When a rotational torque is transmitted from the drive part such as an electric motor, and so forth (not shown in the drawing) to the main shaft 8 to start its rotation, the orbiting scroll member 2 commences its turning. In this case, however, since the orbiting scroll member 2 is prevented from its rotation by the rotation-preventing mechanism 9 provided on it, both stationary scroll member 1 and orbiting scroll member 2 function to compress the operating fluid on the basis of the principle of compression as described in the foregoing in reference to FIG. 1. In this instance, the orbiting scroll member 2 perform its eccentric revolution, the static and dynamic balancing of which is done by the balancer 10. Further, in such scroll compressor, there occurs a thrusting force which tends to separate the stationary scroll member 1 and the orbiting scroll member 2 in the axial direction during compression of the operating fluid. This thrusting force is undertaken by holding the bottom surface of the base plate 2b of the orbiting scroll member 2 on the upper surface of the thrust bearing 7 provided on the bearing frame 6.
The conventional scroll compressor as constructed in the above-described manner increases the fluid pressure towards the center of both stationary and orbiting scroll members during its operation as will be understandable from the operating principle of the scroll compressor shown in FIG. 1, whereby the base plate 2b of the orbiting scroll member 2 is deformed ithe center-convexed shape by an amount .delta..sub.1, for example, owing to a load exerted by the compressed gas, as shown in FIG. 3(b). On account of this, the bottom surface of the base plate 2b of the orbiting scroll member 2 and the inner peripheral edge of the upper surface of the thrust bearing 7 bring about concentrated sliding contact. By this phenomenon taking place during the operation of the compressor, this sliding part becomes apt to readily bring about abnormal wear or seizure with the consequent various problems to occur such that the compressor is damaged, mechanical loss of the compressor increases, and so on. Such sliding phenomenon appears consequently when the upper surface of the thrust bearing or the base plate 2b of the orbiting scroll member 2 is in the center-convexed shape at its inner peripheral side with respect to the outer peripheral side thereof owing to its state at the time of machining, etc. as shown in FIGS. 4(a), 4(b), 5(a) and 5(b), or when both upper surface of the thrust bearing 7 and bottom surface of the base plate 2b are in the center-convexed shape at their inner peripheral side with respect to the outer peripheral side, all these having been liable to bring about abnormal friction, seizure and other undesirable phenomena in the thrust bearing.